Polyurethane foam is increasingly being used as a sealant in both residential and commercial building construction for sealing spaces between door and window frames, in addition to more traditional uses such as insulation. When used as an insulator, polyurethane foam essentially fills any air space between the wall frames of a structure and thereby allows such insulated buildings to require substantially less energy to keep heated or cooled. Further, the foam can be sprayed to insulate spaces as a substitute for electric space heaters.
Polyurethane foam for on-site applications is typically supplied as a “single-component” foam or as a “two-component” foam. With both types of foam, the chemicals which create the foam are typically carried in portable containers, i.e. pressurized cylinders, and applied by an operator via an application gun. For two-component polyurethane foam systems, the two-part products harden by a chemical reaction of a resin and hardener, typically having a relatively short pot life, and may expose users to isocyanates or other toxic compounds. In a two-component foam composition, a reaction between methylene diphenyl diisocyanate (MDI) and glycols takes place directly during the spraying process, which releases to the atmosphere numerous hazardous emissions. During application of a two-component foam, the pressurized cylinders containing the foamable agents and the hardener are connected to a type of spray gun where the components are mixed in appropriate ratios via metering mechanisms contained in the gun and are subsequently sprayed.
There are two principle problems with two-component polyurethane foam systems. One problem is that the guns are typically made of stainless steel and/or brass and contain precise metering mechanisms that must be cleaned shortly after use. The guns must be cleaned shortly after use because in a two-component system, the foam hardens within a relatively short period of time via chemical reaction with the isocyanate hardener. If the foam is allowed to harden within a gun, the relatively costly gun becomes unusable and typically requires disassembly and the replacement of numerous parts in the metering mechanism to return the gun to a usable state.
The other principle problem with two-component polyurethane foam systems is that the isocyanate-based hardener is extremely toxic to the human nervous system. Isocyanates are readily absorbed via inhalation of vapor and skin contact. Therefore, the use of protective clothing and specialized respirators are required by workers applying a two-component polyurethane foam product.
To overcome some of the problems of two-component polyurethane foam systems, one-component foam products have been developed. In a one-component foam product, generally the resin or foamable component and the isocyanate component are supplied in a single pressurized container and dispensed through the container through a valve equipped gun, equipped with a nozzle attached to the pressurized container. With one-component polyurethane foam systems, when the foamable chemicals leave the nozzle reaction with moisture in the air causes the foam to harden. One component polyurethane foam products typically feature less overspray and introduce fewer airborne isocyanates to the atmosphere surrounding the worksite and are otherwise generally less toxic and safer to use than two-component foam systems.
With the development of single-component polyurethane foam systems, a need has arisen in the art for new foam application hardware that takes advantage of the fact that with a single-component system, there is no need to mix chemical components from two pressurized sources in precise ratios. Ideally, a new single-component foam application system would utilize low cost, easily transportable and easy to clean hardware which would allow the use of single-component polyurethane foams in a wider range of applications.
One-component polyurethane foams are used in the construction trades for filling and insulating walls, as well as for acting as a sealant and/or an adhesive. One-component polyurethane foams are particularly well suited for on-site application. They can essentially be used in any other industry where quality insulation is required. On-site applications for polyurethane foam have increased substantially in recent years extending the application of polyurethane foam beyond its traditional usage in the packaging and insulation fields. For example, polyurethane foam is increasingly being used as a sealant in both residential and commercial building construction for sealing spaces between door and window frames, in addition to more traditional uses as an insulation. In cold weather climates, polyurethane foam is now commonly used as an insulator to fill essentially any air space between the wall frames of a structure. Such insulated buildings require substantially less energy to heat than non-insulated buildings.
One-component polyurethane foams play an important role in improving energy efficiency, significantly improving window and door installation tasks. They can also be used for construction purposes (walls/partitions), and thermal insulation of attic floors, roofs, and basements, etc. In the automotive industry, they can be used as heat and noise insulation, as thermal insulation of refrigerators and insulated tank trucks, etc. In ship building, they can be used for heat-insulating of bulkheads, which prevents the formation of vapors.
Further, one-component polyurethane foams are ecologically-friendly because the main reaction of polymerization of polyisocyanate and polyol to form an isocyanate prepolymer takes place inside a pressured spray canister or spray can. The isocyanate prepolymer represents an intermediate stage in the polymerization process. Isocyanate group-containing prepolymers (isocyanate prepolymer), contained in one-component polyurethane foam compositions are known to those of skill in the art. Such prepolymers are commercially available and usually synthesized by the reaction of one or more polyols, such as a polyester or polyether.
However, most commercially available one-component foams come out in a tiny stream, which makes them suitable only for small-scale insulation (insulating cracks, holes, etc.) Therefore, there is a need in the art for a chemical composition for a one-component polyurethane foam having a viscosity and other characteristics that make the product particularly well-suited for being dispensed from a typical aerosol container, i.e. a spray can, and having a cone-shaped stream with a width of approximately 100 mm to approximately 400 mm.
There is also a need for a spray can nozzle capable of dispensing or spraying a one-component polyurethane foam of appropriate viscosity, at the pressures typically available from a spray can (about 3.5 to 12 atm), wherein the nozzle dispenses the foamable product at a mass flow rate of approximately 6 grams per second to approximately 10 grams per second. Experimentation has shown that such a mass flow rate is capable of covering a 1 m2 surface with a foam layer having a thickness of approximately 30-50 mm after an application time of approximately 1 minute.